Integral gas seal for fuel cell gas distribution assemblies and method of fabrication

ABSTRACT

A porous gas distribution plate assembly for a fuel cell, such as a bipolar assembly, includes an inner impervious region wherein the bipolar assembly has good surface porosity but no through-plane porosity and wherein electrical conductivity through the impervious region is maintained. A hot-pressing process for forming the bipolar assembly includes placing a layer of thermoplastic sealant material between a pair of porous, electrically conductive plates, applying pressure to the assembly at elevated temperature, and allowing the assembly to cool before removing the pressure whereby the layer of sealant material is melted and diffused into the porous plates to form an impervious bond along a common interface between the plates holding the porous plates together. The distribution of sealant within the pores along the surface of the plates provides an effective barrier at their common interface against through-plane transmission of gas.

BACKGROUND OF THE INVENTION

The Government has rights in this invention pursuant to Contract NumberDE-AC01-78ET15366 awarded by the U.S. Department of Energy.

The present invention relates to improved gas distribution assembliesfor use in fuel cells, fuel cells employing such elements, and processesand apparatus for making such elements.

Reference is hereby made to other related patent applications which areassigned to the same assignee as the present application; application ofH. Feigenbaum and A. Kaufman entitled "Integral Gas Seal For Fuel CellGas Distribution Plate", Ser. No. 430,453, filed on 9/30/82; applicationof H. Feigenbaum and S. Pudick entitled "A Process For Forming IntegralEdge Seals In Porous Gas Distribution Plates Utilizing A VibratoryMeans", Ser. No. 430,291, filed on 9/30/82 and application of H.Feigenbaum, S. Pudick and R. Singh entitled "Edge Seal For Porous GasDistribution Plate Of A Fuel Cell", Ser. No. 430,142, now U.S. Pat. No.4,450,212 filed on 9/30/82.

Fuel cell design and operation generally involves conversion of ahydrogen-containing fuel and some oxidant via an exothermic reactioninto D.C. electrical power. This reaction is well-known and hasestablished parameters and limitations. It has been known for some timethat fuel cells can be extremely advantageous as power supplies,particularly for certain applications such as a primary source of powerin remote areas. It is highly desirable that any such cell assembly beextremely reliable. Various fuel cell systems have been devised in thepast to accomplish these purposes. Illustrative of such prior art fuelcells are those shown and described in U.S. Pat. Nos. 3,709,736,3,453,149 and 4,175,165. A detailed analysis of fuel cell technologycomparing a number of different types of fuel cells appears in the"Energy Technology Handbook" by Douglas M. Consadine, published in 1977by McGraw Hill Book Company at pages 4-59 to 4-73.

U.S. Pat. No. 3,709,736, assigned to the assignee of the presentinvention, describes a fuel cell system which includes a stackedconfiguration comprising alternating fuel cell laminates andelectrically and thermally conductive impervious cell plates. Thelaminates include fuel and oxygen electrodes on either side of anelectrolyte comprising an immobilized acid. U.S. Pat. No. 3,453,149,assigned to the assignee of this invention, is illustrative of such animmobilized acid electrolyte. The fuel cells further comprise gasdistribution plates, one in electrical contact with the anode and one inelectrical contact with the cathode. The gas distribution plates conductthe reactant materials (fuel and oxidant) to the fuel cell.

In order to electrically interconnect a group of discrete cell to formone larger fuel cell stack, bipolar assemblies are commonly used. Forinstance, in U.S. Pat. No. 4,175,165, assigned to the assignee of thepresent invention, a stacked array of fuel cells is described whereinreactant gas distribution plates include a plurality of gas flowchannels or grooves for the distribution of the reactants. The groovesfor the hydrogen gas distribution are arranged orthogonally relative tothe grooves for the oxygen distribution.

The gas distribution plates themselves, whether they are part oftermination assemblies having individual distribution plates for one orthe other of the reactants or bipolar assemblies having two distributionplates for distributing both reactants in accordance with thisdisclosure, are formed of an electrically conductive imperviousmaterial. Where bipolar plates are prepared from a non-porous material,such as aluminum, the plate is typically coated with a layer ofnon-corrosive material, such as gold, so as to effectively isolate itfrom the corrosive agents, such as the electrolyte, within the fuel cellenvironment. In more recent fuel cell designs, the gas distributionplates of such assemblies are formed of a porous material so that a moreuniform and complete flow of gas over the electrode surface is provided.

In previous systems wherein nonporous gas distribution plates wereutilized, the reactants always flowed only through the grooves and werecontained by the walls thereof. However, in the more recent systemsutilizing porous plates, it has been necessary to seal the porous platesalong the edges, and in bipolar assemblies, to segregate the reactantsfrom one another to avoid their unintended mixing which could cause thecells to operate improperly or fail altogether.

Various techniques for sealing such porous gas distribution plates areknown. In one such approach, an impervious plate is placed between thegas distribution plates forming a bipolar assembly to prevent thereactants from mixing together. In another prior art approach, a sealedbipolar plate is made up of a porous carbon plate layer which is firstgrooved to provide the reactant channels. Then, five or six layers ofsuitable material such as a resin or carbon material are placed on orimpregnated into all surfaces. However, in this arrangement, the sealinglayer is very thin and if damaged, exposes the original porosity of theporous carbon plate. Although this technique precludes unintended gastransmission, it can result in inadequate electrical contact betweensuch contiguous layers and cells.

In the area of cooling assemblies typically used in larger stacks offuel cells, a technique has been devised in which a sealant film andadditional conductive materials are sandwiched between two plates toprovide a bridging electrical contact across the interfacial boundarywhich separates them. This technique is disclosed in a copending,commonly assigned, U.S. Application entitled "Film Bonded Fuel CellInterface Configuration" by A. Kaufman and P. Terry, Ser. No. 430,148,filed on 9/30/82. This arrangement provides effective containment offree electrolyte, a corrosive agent, from the cooling assembly as wellas good electrical conductivity. However, it is readily apparent thatthis approach introduces additional components at the interface of suchplates which can complicate manufacture and assembly.

A number of techniques have been disclosed in the prior art relating tothe preparation of plates in fuel cells. These include U.S. Pat. Nos.2,969,315; 3,223,556; 3,479,225; 3,779,811; 3,905,832; 4,035,551;4,038,463; 4,064,322; and 4,311,771. For instance, the U.S. Pat. No.2,969,315 patent discloses a fuel cell configuration in which a bipolarplate is fabricated by deposition of two layers of porous nickel onopposite sides of a common support. This common support effectivelyprecludes gas transmission between the two porous nickel layers. Each ofthe two porous layers can be formed from a nickel powder by sinteringthe powder on the support layer.

The U.S. Pat. No. 3,223,556 patent discloses a fuel cell configurationin which a gas impermeable layer, moistened with electrolyte, isdisposed intermediately between two layers of porous material containingthe deposited catalyst on its respective surface opposite the gasimpermeable layer. Electrical contact between these porous layers isachieved through an external circuit which connects an electrical gridwithin each catalyst to an incandescent lamp. The gas impermeable memberwhich separates each of the porous plates from one another does notapparently bond the two porous plates to the other. The physicalintegrity of this composite is maintained by some other means.

The U.S. Pat. No. 3,479,225 patent discloses air and oxygen depolarizedelectrochemical units for electrochemical generation of electriccurrent. This device is of a modular cell construction having areplaceable modular anode. The anode illustrated for this device isitself of a composite construction whereby two separate parallel platesof the anode module are bisected by an insulating layer. This insulatinglayer is gas transmissive but exclusive of fuel transfer therebetween.The 771 patent discloses a permselective bipolar membrane forelectrodialyte cells, the permselective membranes comprising two layersof weakly dissociated ion exchange materials in intimate contact withone another.

The U.S. Pat. Nos. 3,779,811, 4,064,322, and 4,038,463 patents disclosea system for maintaining the proper fluid balance within a fuel cell byseparation of the volume tolerance of the cell from its electrochemicalbalance. This is achieved by providing a porous back-up plate to eachanode and cathode. This plate serves as a reservoir for storing excessfluid produced during the electrochemical reaction of oxygen andhydrogen and for replenishment of electrolyte which is lost as a resultof high temperature operation. Each of the porous back-up plates isconnected to either the anode or the cathode by means of a series ofporous pins. The U.S. Pat. No. 4,064,322 patent discloses that thecatalyst containing layer contiguous to the electrolyte reservoir isimpregnated with a hydrophobic material "to a shallow depth". Thishydrphobic material is impermeable to electrolyte yet permeable to gas,thereby permitting gas accessability to the catalyst.

In the construction of bipolar assemblies, as well as other assembliesused in fuel cells such as current collecting assemblies and coolingassemblies wherein distribution of the reactants takes place, it isapparent that the effective containment of reactant materials isimportant. In such assemblies it is also equally apparent that theassemblies should maintain electrical continuity and, in some cases,also provide a barrier against corrosive agents which are a necessarypart of the stack from reaching those regions within the stack thatwould be adversely affected thereby. Accordingly, the inventiondisclosed herein provides an integral gas seal for gas distributionassemblies for use in fuel cells. It also provides process and apparatusfor making such an assembly.

SUMMARY OF THE INVENTION

In accordance with this invention, a porous gas distribution assembly,such as a bipolar assembly is provided with an integral inner imperviousregion. The impervious region can be formed in two porous plates,preferably carbon, at the interface between the two plates byimpregnating a sealant material therein. When impregnated into theporous plates, the sealant material acts as a bond to hold the platestogether in a single integral bipolar assembly. Grooves may be placed inthe carbon plates on the outer facing surfaces opposite the interfacelayer, the grooves of one plate being substantially perpendicular to thegrooves of the other plate. The impervious region is such to prohibitreactant gases from mixing via through-plane transmission but permitelectrical conductivity from plate to plate through the imperviousregion. A fuel cell, in accordance with the present invention, canemploy a plurality of the porous bipolar gas distribution plateassemblies including the inner impervious regions.

According to one embodiment of the process of the present invention, twoporous plates or lamina and a layer of sealant material positioned inbetween the plates, are provided. Pressure and elevated temperature arethen applied to the plates and layer of sealant material to melt thelayer. The material in the layer impregnates the porous plates as itmelts to bond the plates together. Through the proper selection of filmthickness, pressure and temperature, the thermoplastic sealant filmflows into the pores along the surface of each of the contiguous platesthereby effectively bonding one plate to the other and sealing each suchplate along this common interface against gas transfer. Further, beforethe pressure on the bipolar assembly is removed, cooling is allowed tooccur to a lower temperature.

In one embodiment of this process, a thermoplastic film of sealant suchas polyethersulphone, is sandwiched between two untreated porous carbonplates; this sandwich placed in a hot-press; the temperature of thehot-press elevated so as to heat the composite to a temperature in therange of approximately 500°-700° F.; and, the sandwich compressed undera pressure of approximately 200 to 500 psi. The temperature can bemaintained for a suitable period of time, such as a 1/2 hour, and thelength of the compression cycle can vary with the flow characteristicsof the various sealant materials. Subsequent to the completion of thecompression cycle, the resultant sandwich can be maintained under thecompressive load within the press and cooled to ensure fusion of thelamina prior to release of pressure. The composite bipolar plateresulting from this process can thereafter be further machined toincrease its gas distribution capacity, or, if the porosity of the plateis sufficient, used as is.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with regard to the followingdrawings and description in which like elements have been given commonreference numbers:

FIG. 1 is a schematic representation of a fuel cell assembly comprisinga plurality of stacked fuel cells with intermediate cooling plates andterminal current collecting plates.

FIG. 2 is a perspective view of a portion of the fuel cell assembly ofFIG. 1 illustrating an individual fuel cell having bipolar assemblies ingreater detail.

FIGS. 3a-3c describe prior art methods of forming bipolar plateassemblies used in the fuel cell stack systems.

FIG. 4 is a elevational view of the process of forming a porous bipolargas distribution plate assembly in accordance with the presentinvention.

FIG. 5 is an elevational view of porous bipolar gas distribution plateassembly made in accordance with the process illustrated in FIG. 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An exemplary fuel cell stack assembly 10 employing a plurality of fuelcells 11 in accordance with this invention is now described withreference to FIGS. 1 and 2. Hydrogen gas input manifolds 12 are arrangedalong one side of the stack assembly 10. While a plurality of manifolds12 are shown for each group of fuel cells 11, if desired, a singlemanifold arrangement could be used. The manifolds 12 are connected to asource of hydrogen gas 14. Hydrogen gas collecting manifolds 15 arearranged along the opposing stack side in correspondence with the gasinput manifolds 12. Here again, while a plurality of manifolds 15 areshown, a single manifold could be used if desired. The collectingmanifolds 15 are, in turn, connected to a hydrogen gas discharging orrecirculating system 17. The hydrogen gas from the input manifolds 12flows through gas distribution plates 18 to the collecting manifolds 15.

In a similar fashion, a plurality of oxygen or air input manifolds (notshown) are arranged along the stack side (not shown) connecting the onestack side and the opposing stack side. These oxygen manifolds areconnected to an oxygen source 19. The oxygen may be supplied in the formof air rather than pure oxygen if desired. In a similar fashion, aplurality of collecting manifolds are arranged along the stack side (notshown) opposing the stack side having the oxygen input manifolds andconnecting the respective one stack side and opposing stack side. Thesemanifolds would also be connected to an oxygen storage or recirculatingsystem (not shown). The oxygen or air from the input manifolds (notshown) flows through the oxygen gas distribution plates 20 to therespective collecting manifolds (not shown).

In this embodiment, cooling plates 21 are arranged periodically betweenadjacent fuel cells 11. Three cooling plates 21 are shown arrangedintermediate each four cell 11 array. The cooling fluid flowing throughthe cooling plates 21 can be any suitable material such as a dielectrichigh temperature oil manufactured by Monsanto under the trade name"Therminol." A pump 22 circulates the cooling fluid via conduit 23 andinput manifold 24 into the respective cooling plates 21. The coolingfluid then flows into collecting manifold 25 which is connected to aheat exchanger 26 for reducing the temperature of the cooling fluid tothe desired input temperature. A conduit 27 then connects the heatexchangr back to the pump 22 so that the fluid can be recirculatedthrough the respective cooling plates 21.

The fuel cells 11 and the cooling plates 21 are electrically conductiveso that when they are stacked as shown, the fuel cells 11 are connectedin series. In order to connect the stack assembly 10 to a desiredelectrical load, current collecting plates 28 are employed at therespective ends of the stack assembly 10. Positive terminal 29 andnegative terminal 30 are connected to the current collecting plates 28as shown and may be connected to the desired electrical load by anyconventional means.

Each fuel cell 11 is made up of a plurality of elements and includes ahydrogen gas distribution plate 18 and an oxygen or air distributionplate 20. Arranged intermediate the respective gas distribution plates18 and 20 are the following elements starting from the hydrogen gasdistribution plate 18; anode 31, anode catalyst 32, electrolyte 33,cathode catalyst 34 and cathode 35. These elements 31-35 of the fuelcell 11 may be formed of any suitable material in accordance withconventional practice.

The hydrogen gas distribution plate 18 is arranged in contact with theanode 31. Typically, the anode comprises a carbon material having poreswhich allow the hydrogen fuel gas to pass through the anode to the anodecatalyst 32. The anode 31 is preferably treated with Teflon(polytetrafluoroethylene) to prevent the electolyte 33, which ispreferably an immobilized acid, from flooding back into the area of theanode. If flooding were allowed to occur, the electrolyte would plug upthe pores in the anode 31 and lessen the flow of hydrogen fuel throughthe cell 11.

The anode catalyst 32 is preferably a platinum containing catalyst. Thecell 11 is formed of an electrically conductive material, such as acarbon based material except for the immobilized acid electrolyte layerwhich does not conduct electrons but does conduct hydrogen ions. Thevarious elements, 18, 31-35, and 20 are compressed together under apositive pressure. The electrolyte 33, such as phosphoric acid, isimmobilized by being dispersed in a gel or paste matrix so that the acidis not a free liquid. An exemplary electrolyte matrix could comprise amixture of phosphoric acid, silicon carbide particles and Teflonparticles.

The cathode catalyst 34 and the cathode 35 are formed of the same typesof materials as the respective anode catalyst 32 and anode 31.Therefore, the anode 31 and the cathode 35 comprise porous carbon andthe anode catalyst 32 and cathode catalyst 34 can comprise a platinumcontaining catalyst. The cathode 35 can also be treated with Teflon toprevent the electrolyte from flooding back into the porous carboncomprising the cathode.

All of the elements of the cell 11 are arranged in intimate contact asshown in FIG. 2. In order to provide an electrically interconnectedstack assembly 10, bipolar assembly 36 is used to connect togetheradjacent fuel cells 11. A bipolar assembly 36 is comprised of a hydrogengas distribution plate 18 and an oxygen or air distribution plate 20bonded together at inner impervious interface region 37 showncross-hatched. Therefore, a bipolar assembly 36 is comprised of thehydrogen gas distribution plate 18 of one cell 11 and the oxygen or airgas distribution plate 20 of the next adjacent cell 11. The interfaceregion 37 will be described in more detail hereinafter in connectionwith the description of FIGS. 4 and 5.

In order to facilitate the gas flow in the gas distribution plates 18and 20, respective channels or grooves 38 or 39 are employed. Thegrooves 38 in the hydrogen gas distribution plate 18 are arrangedorthogonally to the grooves 39 in the oxygen or air gas distributionplate 20. This allows the grooves to be easily connected to respectiveinput and output manifolds 12 and 15, for example, on opposing sides ofthe cell stack assembly 10. Although grooves within a particular plate,such as plates 18 or 20, are shown as extending in a unidirectionalmanner in FIG. 2, there also can be cross-channels made between thesegrooves to aid in the distribution of the fluidic reactant materials.When such cross-channels are utilized, the primary flow of reactants isstill in the direction of the grooves 38 and 39 shown in FIG. 2; thatis, in the direction that the reactants flow between the reactant'sinput and collecting manifolds.

The gas distribution plates 18 and 20 supply the respective hydrogen andoxygen or air gases to the surfaces of their respective anode 31 orcathode 35. In order to more evenly distribute the respective gases atthe anode 31 or cathode 35 plate surfaces, the gas distribution plates18 and 20 are formed of a porous material such as porous carbon. Thisallows the respective gases to flow through the pores of the plates 18and 20 between the respective channels 38 or 39 to provide more uniformgas distribution over the face of the respective anode 31 or cathode 35.

Referring now to FIG. 3, prior art methods of forming bipolar assembliesare briefly described. In FIG. 3a, assembly 300 of three plates, calledthe A-B-A assembly, is shown comprising two grooved porous carbon plates302 and 304 and an impervious plate 306 positioned between plates 302and 304. The grooves in the carbon plates are gas distribution channels,each plate's channels (channels 308 in plate 302, the channels in plate304 are not visible in this figure) being substantially perpendicular toeach other. The two porous plates are generally sealed along their edgesso that the reactants cannot escape and mix with each other. Theimpervious plate 306 prevents reactants from through-plane transmission;that is, passage from porous plate 304 to porous plate 302 through theplane of impervious plate 306. Electrical conductivity between theplates 302 and 304 must be preserved, however. The A-B-A assemblyrequires the addition of the plate 306, thereby causing extra steps inbonding the assembly together and increasing the size of the assembly bythe thickness of the impervious plate 306.

FIG. 3b shows another prior art approach to providing a bipolarassembly. A single channeled porous carbon gas distribution plate 320 isshown although in use it is assembled with another such plate to form abipolar assembly. After the channels 322 are made, five or six layers ofa suitable material such as a resin or carbonized material are placed onor impregnated into all surfaces. This technique substantiallyeliminates the surface porosity of the plate and significantly reducesthe plate's ability to receive and store acid. Also, the sealing layeron the plate is quite thin and if damaged could reexpose the pores insealing layer surface of the plate thereby providing a passage forunwanted through-plate transmission of reactant gases.

Finally, FIG. 3c shows a plating approach to bipolar assemblyconstruction. A non-porous aluminum plate 330 is used for gasdistribution which has grooves 332 for reactant gas channels. Since thealuminum plate is not porous, it is unlikely to permit the unintendedescape of reactants. However, this type of plate does not providesurface porosity for better distribution of reactant gases to theelectrodes. Also, the aluminum is subject to corrosion from theelectrolyte used in the cell. To prevent this, a layer of non-corrosivematerial 334 has to be placed over the entire plate. Gold plating isused for this purpose and is obviously quite expensive.

Referring now to FIGS. 4 and 5, the hot press method for manufacturingthe integral impervious region 37 of FIG. 2 is described in connectionwith FIG. 4. In FIG. 4, two porous gas distribution plates 402 and 404are shown with a layer of thermoplastic sealant material 406 positionedbetween. The assembly of plates 402 and 404 and layer of sealantmaterial 406 are pressed together under pressure in a press 410. Thetemperature of the assembly is elevated to a relatively high temperaturewhile the pressure is being applied causing the layer of sealantmaterial 406 to melt and diffuse into the pores of the plates 402 and404. The sealant material forms an integral impervious region 500, asshown in FIG. 5, at the interface 502 of plates 402 and 404. Interface502 is formed by pressing the plates 402 and 404 together into contactafter the melting and diffusion of the layer 406.

When the proper amount of thickness of layer 406, pressure and elevatedtemperature are used, the layer completely impregnates the adjacentplate surfaces to form the impervious region 500 leaving substantiallyno sealant material between adjacent plate surfaces. Intimate contact atthe interface 502 of the plates 402 and 404 thereby results to providegood electrical conductivity. The pressure from press 410 preferablycontinues to be applied while the plates 402 and 404 are allowed to coolto a lower temperature. This process results in the plates 402 and 404being bonded and held in electrical contact by an impervious region 500to form a single porous bipolar gas distribution plate assemblydesignated generally 510 in FIG. 5. The plates 402 and 404 have goodsurface porosity, no through-plane porosity for the transmission ofreactants across interface 502, but good through-plane electricalconductivity between the plates.

The porous plates 402 and 404 are preferably porous carbon plates. Forinstance, the plates can be reticulated vitreous carbon (RVC) plates;needled-felt plates; or graphite plates. RVC plates have relativelylarge pores, approximately 0.1 to 1.0 millimeter size, whileneedled-felt plates have relatively small pores approximately 0.01 to0.1 millimeter size. Graphite plates can be made of the same material asthat commercially available for use as industrial graphite electrodes.They are molded or extruded elements made from graphite particles.Graphite plates have relatively very small pores, approximately 0.001 to0.01 millimeter size. The graphite material is the preferred materialfor use as plates 402 and 404.

Porous plates are preferred because cross grooves can be eliminated,reactants can move around the clogs that may be formed in some of thepores, and any electrolyte in the area can be taken up. When designingthe bipolar assembly, a balance must be made among all of the abovefeatures, a balance must be made among all of the above features as anaid in selecting optimum pore size.

Any suitable material, including electrically insulating materials, canbe used for the sealant material. For instance, suitable thermoplasticresin materials can be used. However, the operating temperature of thefuel cell, the nature of the corrosion-producing conditions in the cell,etc., may require the materials used to be selected more carefully. Forinstance, when a hot electrolyte such as phosphoric acid at temperaturesof about 350°-450° F. is used in the cell, suitable candidate materialsinclude FEP Teflon (fluorinated ethylene-propylene), polyparabanic acid,polyethersulphone, polysulphone, polyphenylsulphone and PFA Teflon(perflorinated alkoxy tetrafluoroethylene). The material providesimpervious bond between the porous plates 402 and 404 after assimilationinto the bipolar assembly and yet does not interfere with electricalconductivity. Suitable candidate materials for such use are FEP Teflon(flouroinated ethylene-propylene), polyparabonic acid andpolyethersulphone.

The pressure applied to the two carbon plates 402 and 404 by press 410must be great enough to force the two opposite surfaces of the platestogether into intimate contact but must not be so great as to crush theplate material. In using RVC for plates 402 and 404, the pressure waslowered to approximately 200 psi since RVC material in very brittle andmay crack at higher pressures. This may lead to a reduction inelectrical conductivity when RVC is used since the points of contact onthe adjoining surfaces would be fewer. In using nettled-felt platematerial, a pressure of about 1260 psi was used.

Once the assembly of plates and layer of sealant material are placed inthe press 410, the temperature is elevated to within a range of betweenapproximately 500° and 700° F., but preferably about 650° F. plus orminus 20°. Generally it takes three or four minutes for the assembly andthe press to heat up to the elevated temperature and stabilize from theambient room temperature during the melting of the layer 406.

After heating takes place for the alloted time, the assembly is cooled,generally to about 350° F. under pressure. Cooling can take placenaturally by turning off the heater, or by forced cooling such as byutilizing fans or a water spray. Cooling is continued until the sealantis sufficiently solidified at which time the pressure on the assemblycan be removed.

The dynamics of the hot-pressing cycle causes the sealant film to flowinto the pores along the surface of each of the porous plates therebyeffectively sealing the surface of each such plate along its commoninterfacial boundary with the other without significant loss orimpairment of the porous plate storage and/or gas distribution capacity.Since the sealant film has been redistributed within the pores os eachsuch contiguous plate, or lamina, the distance between each such platehas been reduced, thus, maintaining continuity of electrical contacttherebetween. Subsequent to the completion of the hot-pressing cycle,the compression of the sandwich can be maintained until the sandwich isadequately cooled to a temperature which results in solidification ofthe sealant within the pores.

Any suitable thickness of sealant material can be used to form theplate. It has been found that thicknesses of about 0.005 to 0.020 incheshave produced bipolar plates with good sealing ability. It has also beenfound that when the thinner sealant layers are used, it is preferable toassure that the surfaces of the plates are relatively flat. They can bemade flat by sanding or some other suitable technique.

One example of a bipolar assembly produced by the process of theinvention is as follows. A needled-felt carbon material approximately0.100 to 0.125 inches thick, as supplied by Pfizer, Incorporated, wasused for the gas distribution plates. A layer of polyethersulphonesealant material approximately 0.020 inches thick was placed between theplates. The carbon plate-sealant assembly was then held together atapproximately 500 lbs. per square inch at between approximately 500° and700° F. for approximately 1/2 hour. The assembly was then allowed tocool to approximately 300° F. under a pressure of approximately 500 lbs.per square inch. Using a 0.0200 inch thick layer of polyethersulphone,the resulting bipolar assembly was leak-tested with good results.

Another example of a bipolar assembly produced by the process herein isusing an extruded Great Lakes' carbon-type HLM plate having relativelyfine pores for the gas distribution plates. A layer of polyethersulphonesealant material approximately 0.005 inches thick was placed between theplates. The sealant-plate assembly was then subjected to a pressure ofabout 900 lbs. per square inch and a temperature of about 700° F. forabout one hour. With the pressure still applied, the assembly was thencooled to about 300° F. and then the pressure released. Another platematerial used in this process was an Airco Spear 940G extruded graphitematerial. This latter material was found to be less expensive andexhibited better corrosion resistance as compared to the HLM plate.

To facilitate distribution of the reacting gases, grooves may be placedin each of the porous plates, the grooves typically being approximately1/16 of an inch deep and approximately 1/16 of an inch wide. If theporous structure in the carbon plates is sufficiently open, the groovesare not necessary. However, grooves are preferred, as are additionalcross grooves to help overcome clogs and obstructions occurring in thecarbon plates which may cut off flow of the reactants.

The patents and publications described herein are intended to beincorporated by reference herein. The invention may be embodied in otherforms or carried out in other ways without departing from the spirit oressential characteristics thereof. For instance, current collecting andcooling assemblies having porous plates for distributing reactants therethrough can also be manufactured as, and embody the structure, describedhere. If the other elements of the current collecting assemblies andcooling assemblies are made of impervious materials, such as aluminum,the further purpose of interfacial region 37 within the porousdistribution plate can be to prevent corrosion of the aluminum plate bythe electrolyte as well as bonding the aluminum and porous platestogether.

It is understood that a great number of combinations of temperature,pressure, and sealant materials can be utilized to make a desirableassembly. The temperature used should be sufficient to enable thesealant to flow into the pores of the plate. The pressure applied shouldbe of sufficient value to place the two plate members in contact as thesealant flows into the pores. However, the pressure should not be sogreat as to cause crushing or other types of damage to the plates.

It should be understood that the foregoing description is onlyillustrative of the invention. Various alternatives and modificationscan be devised by those skilled in the art without departing from theinvention. Accordingly, the present invention is intended to embrace allsuch alternatives, modifications and variances which fall within thescope of the appended claims.

What is claimed is:
 1. An assembly for distributing reactant materialsin a fuel cell comprising two adjacent electrically conductive platemembers forming an interface therebetween where they contact each other,at least a first of said plate members being made of a porous materialsuitable for distributing reactant material from a surface thereof otherthan its surface forming said interface with the other plate member, thetwo plate members being integrally bonded to one another at theirinterface with a sealant material residing in the pores of said firstplate member in the region of said interface whereby the two platemembers maintain electrical contact with one another while preventingthe reactant material from passing from said first plate to said otherplate through said interface.
 2. An assembly as in claim 1 wherein saidother plate member is made of a porous material suitable fordistributing another reactant material from a surface thereof other thanits surface forming said interface with the first plate member therebyforming a bipolar distribution assembly and, further, wherein saidsealant material also resides in the pores of said other plate memberalong said interface region thereof.
 3. An assembly as in claim 1wherein each of said porous plates includes a plurality of substantiallyparallel grooves, the grooves of one plate being disposed substantiallyorthogonally to the grooves of the remaining plate.
 4. An assembly as inclaim 1 wherein said porous plate member is made of a reticulatedvitreous carbon material.
 5. An assembly as in claim 1 wherein saidporous plate member is made of needled-felt carbon material.
 6. Anassembly as in claim 1 wherein said porous plate member is made ofgraphite.
 7. An assembly as in claim 1 wherein the sealant material is athermoplastic resin material.
 8. An assembly as in claim 1 wherein saidsealant material is selected from the group consisting of fluorinatedethylene-propylene, polysulphone, polyethersulfone, polyphenylsulphone,perflorinated alkoxy tetrafluoroethylene, and mixtures thereof.
 9. Afuel cell stack comprising a plurality of fuel cells and having at leastone bipolar distribution assembly comprising two adjacent, electricallyconductive, plate members forming an interface therebetween where theycontact each other, the plate members being made of a porous materialeach suitable for distributing different reactant materials to a fuelcell from a surface thereof other than their surfaces forming saidinterface, the two plate members being integrally bonded to one anotherat their interface with a sealant material residing in the pores of saidplate members in the region of said interface whereby the sealant bondsthe two plate members together while electrical contact is maintainedbetween the plates and the different reactant materials are preventedfrom passing through said interface to mix with each other.
 10. In afuel cell stack assembly comprising a plurality of adjacent individualfuel cell units having contiguous porous gas distribution plates to forma bipolar assembly, the plates being separated from one another by a gasimpermeable, electrically insulating barrier, whereby electrical contactis maintained between such plates, the improvement comprising:acomposite bipolar assembly wherein contiguous electrically conductiveporous plates are bonded in contact with one another along a commoninterface with a relatively insulating, thermoplastic sealant means; andsaid sealant means being principally distributed within the pores ofeach plate along said common interface to maintain substantial contactbetween said plates along said common interface whereby a securephysical union of each of said plates to the other with substantialelectrical contact is maintained therebetween and a gas impermeablebarrier is provided so as to prevent diffusion of reactants from oneplate to the other across their common interface.